Making Sense Mechanisms Described Here

BOOK REVIEW There have been key stages in unlocking many of the transduction Making sense mechanisms described here. The discovery, by patch recording, in the Sensory Transduction mid-1980s that rod membranes contained cyclic nucleotide–gated channels, and that the internal second messenger from the visual pig- by Gordon L Fain ment was cGMP and not calcium (as was then widely believed), came Sinauer Associates, 2003 as a great surprise. Understanding rods and cones also means know- ing how currents circulate around the cells. The enabling technology 340 pp. cloth, $24.95 there was learning how to suck a cell into, rather than onto, a pipette. ISBN 0878931716 Olfactory cells suddenly became objects of intense scrutiny when Reviewed by Jonathan Ashmore patching also showed cyclic nucleotide–gated channels on their cilia and molecular biological studies revealed a profusion of odor receptors. For hair cells in the ear, the enabling step may have come a little earlier when it became possible to deflect the sensory hair bundle of individual cells through piezoelectric manipulation (an approach What you know about this page so far has come to you through now ‘rebranded’ as nanotechnology). your senses. Batteries of sensory cells—and not just in your eye— The book is a model of how to use simple, uncluttered diagrams. http://www.nature.com/natureneuroscience have been used to ensure that you, gentle reader, are still reading The minor quibbles hardly bear mentioning. Sensory hair cells do and not mopping up coffee that you have just spilled down your not all have kinocilia; they do not in the adult mammalian cochlea. front. Understanding the processes whereby physical stimuli, light, Sentences such as “there are 12 million olfactory cells in a human mechanical displacements, odor and taste chemicals, and so on are but 4 billion in a German shepherd” tax those of us who do not converted into codes for the nervous system is what studies of the know our dogs. It could also have been helpful to have had more physiology of sensation are all about. The surprise is that, until about noise in sensory systems—which arises, for example, because recently, many of the cellular mechanisms have been opaque to light is made of discrete photons and odors of molecules, or nonspecialists and specialist researchers alike. because thermal fluctuations make molecules vibrate. The surprise Sensory Transduction concentrates firmly on how sensory receptor is that most sensory receptors operate at the limits set by physical cells work. Gordon Fain, one of the central players in the unraveling laws. Although many sensory systems have evolved to operate at of phototransduction, takes the position that we have now, thanks to these limits, it is often necessary to navigate through the detail to some genetics, molecular biology and cell physiology, ‘cracked the re-emphasize this important feature. problem’. His strategy, unashamedly, is to describe cellular mecha- What emerges from Sensory Transduction is that there are still © 2004 Nature Publishing Group nisms of transduction, emphasizing a molecular unity and how this underexplored cellular mechanisms in the more ‘exotic’ senses links to other branches of neuroscience. The central claim, and it is a (exotic to us, if not the animals concerned; consider electrorecep- remarkable one, is that we know in outline how sensation occurs in all tion or magnetoreception). The last few years have revealed the the major senses of the body and that this is one of the great achieve- molecules for temperature sensing, and this is well described. But, ments of physiology and neuroscience in the twentieth century. although we know some of the key channels in touch sensation, It does not take much to realize that, in our anthropocentric way, there the detail still has to be filled in. At the core of our under- we know more about transduction in vertebrate systems than in standing of hearing and balance, despite the most strenuous invertebrates. Sensory Transduction does attempt to redress this efforts, the vertebrate hair cell transducer channel—the first step in imbalance. The kinds of senses possessed by bacteria or unicellular mechanical displacement sensing—has stubbornly resisted identi- organisms inspire a sort of astonishment that so much can be fication. The reasons are not hard to identify. Hearing depends on packed into so little. Here we can learn about chemotaxis by way of relatively few tranducing channels and hair cells. And the tradi- introducing smell, or about the literature of fly gustation as an tional assay, described in this book as cloning followed by func- introduction to our sense of taste. The approach is pursued with a tional expression, is a significantly harder proposition for fiddly light touch (no joke). The book can be read by anyone with a basic mechano-sensing channels. knowledge of neuroscience along with a smattering of electrophys- If you want to understand how different sensory cells work, this is a iology and molecular biology. The membrane biophysics that you broad-ranging and accessible book. The delight is, for once, to find need (or knew and have forgotten) is supplied engagingly in an not just a cluster of chapters on the senses buried in a more general early chapter. The combination provides a simple way of making text but a book written by a single author, which makes it almost you a connoisseur of biological engineering in vertebrate and unique. Although it is directed probably at the graduate level or invertebrate systems. above, there is much that an undergraduate could take away from reading this volume, and it succeeds in summarizing the enormous Jonathan Ashmore is in the Department of Physiology, University College strides of recent years. The book even starts with a Homeric maxim London, London, UK. and dedication. (I do confess that I had to look that up.) But having e-mail: [email protected] got that far, you, too, will have to read the rest. í NATURE NEUROSCIENCE VOLUME 7 | NUMBER 2 | FEBRUARY 2004 95.

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